Alternators are well known and are commonly used in, for example, automobiles and the like to charge a battery of the automobile and to power the automobile's electrical system when the engine of the automobile is running. It is also well known to use voltage regulators to modulate the small field current of the alternator in order to produce a constant voltage at the output of the alternator.
FIG. 1 illustrates an example of a known alternator arrangement 100, comprising an alternator 110 and regulator 120, operably coupled in parallel across a battery 130. Typically, the alternator 110 comprises a rotating magnet called the rotor, which is operably coupled to the engine, and caused to rotate when the engine is running. The rotor rotates within a stationary set of conductors wound in coils about an iron core called a stator. The magnetic field of the rotor cuts across the conductors, generating an electrical current. This electric current may then be used, for the example illustrated in FIG. 1, to charge the battery 130, as well as to power the automobile's electrical system (not shown for clarity purposes only).
Alternator arrangements such as the alternator arrangement 100 of FIG. 1 are required to generate power when the engine is idling, as well as when the engine is running at high speed. Accordingly, in order for the alternator to generate sufficient power when the engine is idling, the alternator is typically coupled to the engine via a belt or the like. The rotor of the alternator rotates at a sufficient speed to for the alternator to generate sufficient power, even though the engine is turning over at a low speed. However, when the engine is turning over at high speeds, the rotor of the alternator rotates at much greater speeds. As will be appreciated by a skilled artisan, when rotating at greater speeds, the magnetic field generates more current in the stator.
For automotive alternators, the rotor magnetic field is generally created by way of a field winding, which allows control of the alternator-generated current by varying the current in the rotor filed winding. Accordingly, the regulator 120 of FIG. 1 provides a field current modulation signal (fcmod) to the alternator 110. In this manner, the regulator 120 is able to regulate the current generated by the alternator by monitoring the voltage at Vbat, and modulating the field current to control the output of the alternator 110.
A known problem with automotive alternator arrangements and the like is that they generate heat, in particular when operating at high speeds. Although such alternator systems are typically provided with some form of cooling system, such cooling systems may not always be capable of dissipating the heat generated. In the case where heat is not sufficiently dissipated, the various elements within the alternator system can overheat, causing damage not only to those elements, but to other coupled elements as well.
To overcome this problem, it is known for alternator regulators to be operably coupled to temperature sensors such that, when the temperature exceeds a threshold, the regulator is able to cut off the field current to the alternator, effectively switching off the alternator, and thus substantially preventing the generation of more heat.
A problem with such known techniques for avoiding overheating of components within an alternator system is that, in order to ensure that the components do not exceed a maximum temperature above which they are susceptible to damage, the threshold at which the regulator cuts off the field current must be set significantly below such a maximum temperature in order to take into account tolerances, etc. in temperature sensors and the like, as well as any latency in the temperature sensing apparatus. As a result, the alternator system will not operate at an optimum capacity.
Furthermore, in cases where the engine is running at high speeds for long periods of time, the alternator will be continuously switched off and on, resulting in further inefficient operation and imposing undue stresses and strain on the various components.
Thus, a need exists for an improved method and apparatus for regulating a field current of an alternator device in which at least some of the above mentioned problems with known methods and techniques are substantially alleviated.